The purpose of this experimental series is to evaluate the time-domain functional changes which occur in the locomotor and postural balance maintenance in sub-human primates after the selective lesion placement in different parts of the body equilibrium system. Dysequilibrium and systemic readjustment, and oculomotor abnormality are examined simultaneosly in quantitative and repeated manners. For the analysis of locomotor deviations the squirrel monkey rail test and the squirrel monkey platform test are used. Furthermore, squirrel monkeys are trained to trot in a motor driven treadmill cage and the EMG recordings obtained from bilateral gastrocnemius and tibialis anterior muscles are to be analyzed, to examine the vestibulo-descending effects. In order to evaluate statokinetic body balance function, the statokinesimetry is presently being developed in conjunction with operant conditioning paradigm. From this experimental situation, EMG recordings are to be obtained. All animals are behaviorally trained and the repetitive acquisition of quantitative and comparable data, along the long time course is feasible. Experimental lesions include peripherl lesions, such as unilateral utricular nerve resection, etc., central lesions, such as a minute lesion placement in the medial vestibular nucleus, etc., and combined lesions. Furthermore, our objective extended to the evaluation of the effect of kinetic proprioceptive input enhancement toward the vestibulo-genic dysequilibrium compensation. All lesions confirmed by light microscopy in order to obtain functional and morphological correlation.